Horizontal drilling method

ABSTRACT

A bore hole support system is formed from a flexible liner that is readily everted within a bore hole and forms a bore hole support system to install a casing in the bore hole while supporting the bore hole walls. After a pilot hole is drilled, the pilot hole is traversed with a reamer to form the pilot hole diameter to a larger diameter for the final bore hole. The flexible liner with the attached casing is everted and pressurized behind the reamer as the reamer traverses the pilot hole to support walls defining the bore hole while pulling the casing into the bore hole. The liner is simply removed from a storage and everting canister and remains with the casing in the bore hole. In certain circumstances, the liner may be coated with a water soluble material so that the casing may be in fluid communication with the bore hole walls when the coating has dissolved.

This is a Divisional of application Ser. No. 08/841,894, filed Apr. 17,1997, now U.S. Pat. No. 5,816,345.

BACKGROUND OF THE INVENTION

This invention relates to drilling horizontal bore holes, and, moreparticularly, to stabilizing horizontal borehole walls.

Many uses arise for horizontal bore holes, particularly in the field ofenvironmental remediation where a geologic structure must be followedfor contaminant monitoring and removal. There are several considerationsrelative to drilling horizontal boreholes. A first consideration isforming the borehole itself, i.e., drilling the passage through theearth. A second consideration is the support of the bore hole walls.Next, as the hole is drilled, the bore hole cuttings must be removedfrom the borehole. The final consideration is the installation of acasing and, optionally, a well screen within the borehole.

In conventional drilling, a drilling mud is circulated around a drillbit in order to flush the cuttings from the drill from the hole. Thedrilling mud is commonly formed of a composition that will form a mudcake on the borehole wall and support the borehole walls againstcollapse. Drilling mud exerts pressure against the hole wall, which thensupports the wall. If the drilling mud cannot support the hole wall, thewalls will collapse and greatly impede emplacement of the casing and anywell screen provided with the casing.

In drilling horizontal holes for remediation of contaminated geologicformations, however, the drilling mud acts to plug the pore space of theformation. The plugging effect of the drilling mud drastically reducesthe permeability of the geologic formation to fluid flow into or out ofthe hole. The plugging effect is especially pronounced in looselyconsolidated sands and gravel that are often the preferred flow paths ofcontaminates in the geologic structure.

It will also be-appreciated that the drilling muds that effectivelysupport the borehole walls also circulate very slowly in large diameterbore holes. This slow circulation velocity reduces the effectiveness ofthe drilling mud to remove the drill cuttings from the borehole.

Patent application Ser. No. 08/769,656, now U.S. Pat. No. 5,803,666,"Horizontal Drilling Method and Apparatus," filed Dec. 19, 1996,incorporated herein by reference, describes a liner system that supportsa bore hole and reduces friction during casing installation in a borehole. The liner system is designed to be removed from about the casingafter casing installation so that the casing and any screens thereon candirectly contact the bore hole walls for communication with thesurrounding structure. But, in many instances, there is no need tocommunicate with the geologic structure and no need for thecomplications associated with liner removal from about an installedcasing.

Accordingly, it is an object of the present invention to provide analternate means for supporting the wall of a borehole during horizontaldrilling.

It is another object of the present invention to avoid the buildup ofmud cake on the bore hole wall and improve the removal of cuttings outof the borehole.

Yet another object of the present invention is to provide a simple linersystem for use in casing installation in a borehole.

One other object of the present invention is to reduce the forces on thehole casing during emplacement in the borehole.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the apparatus of this invention may comprise a bore hole supportsystem. A bore hole casing is provided with first and second ends. Aflexible liner defines a generally cylindrical shape with an interiorand an exterior when everted and has a distal end connected to the firstend of the casing and a proximal end. A canister for housing the linerand the casing in an inverted condition defines an exit end connected tothe proximal end of the liner. A first cord is connected to the secondend of the casing and extends through the canister for inverting theliner with the casing. A second cord is connected to the first end ofthe casing and extends along the exterior of the liner to the canisterfor everting the liner with the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate the embodiments of the present inventionand, together with the description, serve to explain the principles ofthe invention. In the drawings:

FIG. 1 is a pictorial illustration in cross-section of an everting borehole liner for placement with a borehole casing according to oneembodiment of the present invention.

FIG. 2 is an illustration in cross-section of a system for forming afinal bore hole using an everting liner.

FIG. 3 is a pictorial illustration in cross-section of a drill reamer,and everting bore hole liner for use in casing installation.

FIG. 4 is a pictorial illustration of the completed bore hole supportedby an everted liner and the installed casing.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, the bore hole wall supportfunction of drilling mud is replaced with an everting flexible boreholeliner. As shown in FIG. 1, a suitable flexible bore hole liner system 10is formed from a flexible liner 12 with its distal end 24 attached tocasing 26 by a suitable clamp, or the like. Inversion tether 22 isattached to an enclosing reel 16. Proximal end 18 of flexible liner 12is attached to canister 14 by a clamp, or the like. It will beunderstood that the various components may be connected by simplecircular clamps or sleeves, but any convenient means of attachment maybe used.

In the special case when the removal of the liner is not required (e.g.,there is no screen in the casing), the casing can be installed directlyduring liner eversion. Liner 12 is attached directly to a first end ofcasing 26. Casing 26 is plugged at the first end with tapered plug 32.Tether 22 is attached to second tapered plug 28. Tapered plugs 28, 32allow casing 26 to move more easily in canister 14 and liner 12. Plugs28, 32 are preferably equipped with ports to allow the casing to befilled with water, if needed, in order to achieve near-neutral buoyancyfor less friction during eversion from canister 14. Liner 12 is evertedfrom canister 14 to carry casing 26 into the borehole as described forFIGS. 2 and 4.

In an exemplary embodiment, flexible liner 12 and casing 26 are invertedwithin canister 14 by winding cord-like member 22 onto reel 16. Evertingliner systems are well known and are not, per se, the subject of thepresent invention. Everting liner systems are shown in U.S. Pat. No.5,176,207, issued Jan. 5, 1993; U.S. Pat. No. 5,377,754, issued Jan. 3,1995; and U.S. Pat. No. 5,466,093, issued Nov. 14, 1995, allincorporated herein by reference.

In accordance with one aspect of the present invention, as shown inFIGS. 1 and 2, a second cord-like member 34 is fixed to plug 32 incasing 26 and passes about the exterior of liner 12 to proximal end 18of liner 12. As shown in FIG. 1, the proximal end of cord 34 is fixed tocanister 14. Cord 34 can now be pulled to assist in everting liner 12from canister 14. Liner 12 is inflated by introducing a fluid, e.g.,water, through valve 15.

In a particular application, described below, a generally rigid member42, hereinafter called a "pig", includes an attachment point 38, whichmay be a bolt eyelet, pulley, or the like, through which cord 34 passesto assist in everting liner 12 and casing 26. As pig 42 is moved througha bore hole, as hereinafter explained, attachment 38 pulls cord 34 ascord 34 slides through attachment 38 and everts liner 12 and casing 26from canister 14. Pig 42 is generally a conical/cylindrical shape andfurther includes a second attachment point 44 for attaching to a drillstring component.

FIGS. 2 and 3 further illustrate the installation of flexible liner 12within a borehole. Pilot hole 55 is formed conventionally with entranceend 56 and exit end 40. Pilot hole 55 is typically small (2-5 inches indiameter) and is formed by driving a steerable bit (not shown) throughthe earth to exit end 40. Drilling fluids are injected through the bitto support the wall of pilot hole 55 and to remove drill cuttings fromthe hole as the cuttings are generated.

When pilot hole 55 is completed, drill stem 58 extends through end 40and reaming drill bit 52 is attached to the end of drill stem 58. Inaccordance with one aspect of the present invention, pig 42 is attachedto reamer 52 by connection 44, which is preferably a rotatableconnection so that pig 42 does not rotate as reamer 52 is rotated toform a bore hole to the desired final diameter. Drill stem 58 is rotatedby drill rig 62 and pulled back through pilot hole 55 as reamer 52 isrotated and drawn through pilot hole 55. Thus, reamer 52 draws pig 42through enlarged hole 60, which, in turn, pulls cord 34 and everts liner12 and casing 26 into enlarged bore hole 60.

Liner 12 may be pressurized by a fluid, e.g., water, introduced throughvalve 15 to maintain the advancing end of liner 12 in contact with pig42 as reamer 52 reams out pilot hole 55. Pressurized everting liner 12supports and seals the wall of bore hole 60 formed by reamer 52. Thepressure in liner 12 is controlled to be greater than the pressure ofdrilling fluid that is circulating around reamer 42. Thus, the flow ofdrilling fluid in pilot hole 55 is forced to flow along the pilot holesurrounding drill stem 58 and can be maintained at a relatively highflow rate to remove cuttings generated by reamer 52 through holeentrance 56. Further, with liner 12 inflated within enlarged bore hole60, the drilling fluid does not flow into the enlarged hole and cannotform a mud cake on the wall of the enlarged final hole.

The everting, inflated liner 12 supports the wall of the enlarged borehole 60, prevents mud cake formation on the enlarged hole wall 60,reduces the drilling fluid injection into the medium outside enlargedhole 60, improves cutting removal via pilot hole 55 and also preventscuttings from settling out of the drilling fluid, which would otherwiseflow more slowly in the enlarged bore hole.

As further shown in FIG. 2, casing 26 is removed from within canister 14as liner 12 is everted within borehole 60. Liner 12 supports the wallsof bore hole 60 as casing 26 moves through bore hole 60 to preventcollapse of the bore hole walls onto casing 26 and to form a relativelylow friction surface along which casing 26 moves.

FIG. 4 is a pictorial illustration of casing 26 fully installed in borehole 60. The ends of casing 26 extend through entrance end 46 and exitend 40 of bore hole 60. Distal end 24 of liner 12 is at entrance end 46and proximal end 18 is at exit end 40 of bore hole 60. Proximal end 18has been disconnected from canister 14 (FIG. 1) and liner 12 remainswithin borehole 60.

As noted above, liner 12 is pressurized by a working fluid to evertliner 12 and casing 26 from canister 14. Thus, liner 12 is generallyformed of an impermeable material during casing 26 installation. Typicalmaterials include urethane, polyvinyl, coated nylon, fiberglass, andKevlar, or a coated porous fabric, e.g., felt, flannel, or muslin,coated with, e.g., urethane, polyvinyl chloride, teflon, or the like. Insome instances, a casing is provided with screens so the interior of thecasing can communicate with the surrounding geologic structure.

In a particular aspect of the present invention, liner 12 is formed of acoated porous fabric, where the coating dissolves in water. A suitableexemplary coating is polyvinyl alcohol. Then, liner 12 is inflatable forthe initial eversion and casing installation, but forms a waterpermeable structure when the coating dissolves.

The foregoing description of the preferred embodiments of the inventionhave been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and obviously many modifications and variations arepossible in light of the above teaching. The embodiments were chosen anddescribed in order to best explain the principles of the invention andits practical application to thereby enable others skilled in the art tobest utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto.

What is claimed is:
 1. A method for encasing a horizontal bore hole,comprising the steps of:providing an everting liner system with anattached casing at an exit location from a pilot hole having an exit endand an entrance end; locating a reamer at the exit end of the pilothole; and traversing the pilot hole from the exit end to the entranceend with a reamer to form the pilot hole to a diameter for the bore holewhile everting and pressurizing the liner system behind the reamer asthe reamer traverses the pilot hole to support walls defining the borehole with a flexible liner while pulling the casing into the bore hole.